Double Good Blueberry Pie

Combine sugar, cornstarch and salt in a saucepan.
Add water and 2 cups of blueberries.
Cook over medium heat, stirring constantly, until mixture comes to a boil and is thickened. Mixture will be clear and very thick.
Remove from heat and stir in butter and lemon juice.
Cool.
Gently, fold remaining 2 cups raw blueberries into cooled mixture and pour into pie shell.
Chill.
Serve with whipped cream.